Solid-State NMR Investigations of Poly[(acrylonitrile)-rotaxa-(60-crown-20)

Abstract

Solid-state NMR has been used to investigate the structure, dynamics, and morphology of the polyrotaxane prepared by polymerizing acrylonitrile in the presence of 60-crown-20. For solid poly[(acrylonitrile)n-rotaxa-(60-crown-20)x] with x/n = 0.01, the 60-crown-20 was found to be phase-separated, amorphous, and highly mobile at room temperature. 2D WISE NMR revealed the presence of less mobile crown segments that were attributed to those in contact with the rigid PAN phase at the interfacial regions. Compared to unthreaded PAN, the Tg of the host backbone was slightly depressed (90 °C vs 110 °C), as measured by solid-state 1H NMR. These PAN Tg values were undetectable with DSC. Dipolar magnetization transfer (i.e., spin diffusion) experiments on the polyrotaxane revealed typical smallest diameters of 6−8 nm for the 60-crown-20 domains and NMR long periods of 20−26 nm. The long periods were compared with electron density correlation lengths computed from SAXS data. Upon heating the polyrotaxane to 80 °C, th...